Group-III nitride semiconductor laser device, and method for fabricating group-III nitride semiconductor laser device

Abstract

Provided is a group-III nitride semiconductor laser device with a laser cavity enabling a low threshold current, on a semipolar surface of a support base the c-axis of a hexagonal group-III nitride of which tilts toward the m-axis. In a laser structure 13 , a first surface 13 a is a surface opposite to a second surface 13 b and first and second fractured faces 27, 29 extend each from an edge 13 c of the first surface 13 a to an edge 13 d of the second surface 13 b . A scribed mark SM 1 extending from the edge 13 c to the edge 13 d is made, for example, at one end of the first fractured face 27 , and the scribed mark SM 1 or the like has a depressed shape extending from the edge 13 c to the edge 13 d . The fractured faces 27, 29 are not formed by dry etching and thus are different from the conventional cleaved facets such as c-planes, m-planes, or a-planes. It is feasible to use emission of a band transition enabling a low threshold current.

1. A group-III nitride semiconductor laser device comprising:
 a laser structure including a support base and a semiconductor region, the support base comprising a hexagonal group-III nitride semiconductor and having a semipolar principal surface, and the semiconductor region being provided on the semipolar principal surface of the support base; and 
 an electrode being provided on the semiconductor region of the laser structure, 
 the semiconductor region including a first cladding layer of a first conductivity type gallium nitride-based semiconductor, a second cladding layer of a second conductivity type gallium nitride-based semiconductor, and an active layer, the active layer being provided between the first cladding layer and the second cladding layer, 
 the first cladding layer, the second cladding layer, and the active layer being arranged along a normal axis to the semipolar principal surface, 
 the active layer including a gallium nitride-based semiconductor layer, 
 a c-axis of the hexagonal group-III nitride semiconductor of the support base tilting at a finite angle ALPHA with respect to the normal axis toward an m-axis of the hexagonal group-III nitride semiconductor, the angle ALPHA being in a range of not less than 45° and not more than 80° or in a range of not less than 100° and not more than 135°, 
 the laser structure comprising first and second fractured faces, the first and second fractured faces intersecting with an m-n plane defined by the m-axis of the hexagonal group-III nitride semiconductor and the normal axis, 
 a laser cavity of the group-III nitride semiconductor laser device including the first and second fractured faces, 
 the laser structure including first and second surfaces, the second surface being opposite to the first surface, 
 the semiconductor region being located between the first surface and the support base, 
 each of the first and second fractured faces extending from an edge of the first surface to an edge of the second surface, 
 the laser structure having a scribed mark, the scribed mark extending from the edge of the first surface to the edge of the second surface, at one end of the first fractured face, and 
 the scribed mark having a depressed shape, the depressed shape extending from the edge of the first surface to the edge of the second surface. 
 
     
     
       2. The group-III nitride semiconductor laser device according to  claim 1 , wherein an end face of the support base and an end face of the semiconductor region are exposed in each of the first and second fractured faces, and
 wherein an angle between the end face in the active layer of the semiconductor region and a reference plane perpendicular to the m-axis of the support base of the hexagonal nitride semiconductor is in a range of not less than (ALPHA−5)° and not more than (ALPHA+5)° in a first plane defined by the c-axis and the m-axis of the group-III nitride semiconductor. 
 
     
     
       3. The group-III nitride semiconductor laser device according to  claim 1 , wherein the angle is in a range of not less than −5° and not more than +5° on a second plane perpendicular to the first plane and the normal axis. 
     
     
       4. The group-III nitride semiconductor laser device according to  claim 1 , wherein a thickness of the support base is not less than 50 μm and not more than 150 μm. 
     
     
       5. The group-III nitride semiconductor laser device according to  claim 1 , wherein the angle between the normal axis and the c-axis of the hexagonal group-III nitride semiconductor falls within a range of not less than 63° and not more than 80° or within a range of not less than 100° and not more than 117°. 
     
     
       6. The group-III nitride semiconductor laser device according to  claim 1 , wherein laser light from the active layer is polarized in a direction of an a-axis of the hexagonal group-III nitride semiconductor. 
     
     
       7. The group-III nitride semiconductor laser device according to  claim 1 , wherein light in an LED mode of the group-III nitride semiconductor laser device includes a polarization component I 1  in a direction of an a-axis of the hexagonal group-III nitride semiconductor, and a polarization component I 2  in a direction indicated by a projection of the c-axis of the hexagonal group-III nitride semiconductor onto the principal surface, and
 wherein the polarization component I 1  is greater than the polarization component I 2 . 
 
     
     
       8. The group-III nitride semiconductor laser device according to  claim 1 , wherein the semipolar principal surface is slightly tilted in a range of not less than −4° and not more than +4° with respect to any one of { 20 - 21 } plane, { 10 - 11 } plane, { 20 - 2 - 1 } plane, and { 10 - 1 - 1 } plane. 
     
     
       9. The group-III nitride semiconductor laser device according to  claim 1 , wherein the semipolar principal surface is one of { 20 - 21 } plane, { 10 - 11 } plane, { 20 - 2 - 1 } plane, and { 10 - 1 - 1 } plane. 
     
     
       10. The group-III nitride semiconductor laser device according to  claim 1 , wherein a stacking fault density of the support base is not more than 1×10 4  cm −1 . 
     
     
       11. The group-III nitride semiconductor laser device according to  claim 1 , wherein the support base comprises any one of GaN, AlGaN, AlN, InGaN, and InAlGaN. 
     
     
       12. The group-III nitride semiconductor laser device according to  claim 1 , further comprising a dielectric multilayer film provided on at least one of the first and second fractured faces. 
     
     
       13. The group-III nitride semiconductor laser device according to  claim 1 , wherein the active layer includes a light emitting region provided so as to generate light at a wavelength of not less than 360 nm and not more than 600 nm. 
     
     
       14. The group-III nitride semiconductor laser device according to  claim 1 , wherein the active layer includes a quantum well structure provided so as to generate light at a wavelength of not less than 430 nm and not more than 550 nm. 
     
     
       15. A group-III nitride semiconductor laser device comprising:
 a laser structure including a support base and a semiconductor region, the support base comprising a hexagonal group-III nitride semiconductor and having a semipolar principal surface, the semiconductor region being provided on the semipolar principal surface of the support base; and 
 an electrode being provided on the semiconductor region of the laser structure, 
 the semiconductor region including a first cladding layer of a first conductivity type gallium nitride-based semiconductor, a second cladding layer of a second conductivity type gallium nitride-based semiconductor, and an active layer, the active layer being provided between the first cladding layer and the second cladding layer, 
 the first cladding layer, the second cladding layer, and the active layer being arranged along a normal axis to the semipolar principal surface, 
 the active layer including a gallium nitride-based semiconductor layer, 
 a c-axis of the hexagonal group-III nitride semiconductor of the support base tilting at a finite angle ALPHA with respect to the normal axis toward an m-axis of the hexagonal group-III nitride semiconductor, the angle ALPHA being in a range of not less than 45° and not more than 80° or in a range of not less than 100° and not more than 135°, 
 the laser structure including first and second surfaces, the second surface being opposite to the first surface, 
 the semiconductor region being located between the first surface and the support base, 
 the laser structure having first and second scribed marks, the first and second scribed marks being provided at an end of the laser structure and extending along a plane defined by an a-axis of the hexagonal group-III nitride semiconductor and the normal axis, 
 each of the first and second scribed marks having a depressed shape, the depressed shape extending from an edge of the first surface to an edge of the second surface, 
 the end of the laser structure having a fractured face, the fractured face connecting respective edges of the first and second scribed marks with the respective edges of the first and second surfaces, and 
 a laser cavity of the group-III nitride semiconductor laser device including the fractured face.